1. Field of the Invention
The present invention relates to a multiple-mode dielectric resonator having a combined dielectric block provided in a cavity, and to a method of adjusting a characteristic of the resonator.
2. Description of the Related Art
FIG. 23 shows the structure of a conventional dielectric resonator using a transverse magnetic (TM) dual mode. In other figures referred to below, a finely dotted area represents a portion on which a conductor is formed.
This dielectric resonator has, as shown in FIG. 23, a cavity body 1 which functions as a waveguide, and a combined dielectric block 2 which is formed of two dielectric elements 2a and 2b combined into a crossed shape, and which is formed integrally with the cavity body 1 and while being positioned inside with the same. The cavity body 1 and the combined dielectric block 2 are made of a dielectric ceramic. A conductor 3 such as Ag is formed on outer peripheral surfaces of the cavity body 1. Conductor plates (not shown) or portions of a metallic case for accommodating this dielectric resonator are attached to two opening end surfaces around two openings of the cavity body 1.
The dielectric resonator shown in FIG. 23, having two dielectric elements 2a and 2b each resonating in a TM110 mode, functions as a TM dual mode dielectric resonator. One unit of the above-described conventional TM dual mode dielectric resonator, however, can only be used as two independent resonators or as two-stage resonator having two resonators coupled to each other. As three resonators forming one dielectric resonator unit, a TM triple mode dielectric resonator designed to cause three TM110 resonance modes by forming a combined dielectric block having three dielectric elements perpendicular to each other has been proposed. Such a conventional TM triple mode dielectric resonator, however, has a complicated overall structure and requires a high manufacturing cost if an ordinary manufacturing method is used.
The applicant of the present invention has filed the Japanese Patent Application No. 21394/1996 proposing a dielectric resonator which has a combined dielectric block formed of two dielectric elements combined into a crossed shape, and which is designed to use three resonance modes.
On the other hand, in a case where a band-pass filter, for example, is formed of a TM dual mode dielectric resonator, such as that shown in FIG. 23, using two TM110 modes, resonance in a TM111 mode can occur in an attenuation range of the band-pass filter when a particular combination of an external size of the cavity body and a cross-sectional configuration of the dielectric block is used. Because of this phenomenon, it has been difficult to obtain a desirable attenuation characteristic.